The research involves two major projects. The aim of one project is to determine the number, gross structure, and chromosomal locations in normal rat cells and in rat pituitary tumor cells (GH-cells) of the genes for the pituitary hormones, prolactin, growth hormone, and the alpha and beta subunits of thyrotropin. We are currently screening a rat genomic library for recombinant lambda bacteriophages containing these genes. These hybrid bacteriophages will then be employed as probes for chromosomal localization by in situ hybridization. The aim of the other project is to determine the primary site(s) at which thyroid and glucocorticoid hormones act to increase growth hormone synthesis by GH-cells, and to investigate the role of insulin in the synergistic regulation by these two types of hormones of growth hormone gene expression. A recombinant bacterial plasmid containing a DNA sequence coding for rat growth hormone which we have prepared will be employed as a hybridization probe in these studies to follow nuclear and cytoplasmic growth hormone-specific RNA sequences during hormonal induction.